This invention relates to tube support grids for a heat exchanger and more particularly to a tube support grid for a nuclear steam generator.
During the operation of steam generators, if the water chemistry deviates from narrow limits due to such problems as condenser leaks, corrosion of the tubing and the tubing supports is likely to take place in the vicinity of the contact therebetween. In a grid-type support, the relatively large difference in curvature between the tube and the support at the contact location should tend to inhibit the accumulation of chemical contaminants which lead to corrosion, however, the possibility of such an accumulation is not entirely precluded. The corrosion process has in the past led to deformation of the tubing and of the support structure as a result of the volumetric expansion of the products of corrosion denting the tubing and weakening the support structure.
U.S. Pat. Nos. 4,007,899; 3,998,268; 3,746,617 and 3,298,922 all employ spring-type supports for tubes or rods. U.S. Pat. Nos. 4,007,899 and 3,998,268 each utilize springs welded to a bar while U.S. Pat. No. 3,746,617 utilizes slotted tubes as spacers and U.S. Pat. No. 3,298,922 has rings which make point contact with fuel rods. U.S. Pat. Nos. 3,575,236; 3,854,529 and 3,998,268 are arrangements in which the support assembly is assembled during the process of installing the tubes. U.S. Pat. Nos. 3,292,691; 3,854,529; and 3,292,691 do not provide sufficient compliance of the supporting surfaces to prevent tube denting while other of the patents hereinbefore mentioned that have compliant support surfaces have a large amount of welding therein.